ConvertLongitude function

Converts between longitude conventions

Converts longitude from [0, 360) to [-180, 180) and vice versa.

ConvertLongitude(lon, group = NULL, from = NULL)

Arguments

• lon: numeric vector of longitude
• group: optional vector of groups (the same length as longitude) that will be split on the edges (see examples)
• from: optionally explicitly say from which convention to convert

Returns

If group is missing, a numeric vector the same length of lon. Else, a list with vectors lon and group.

Examples

library(ggplot2)
library(data.table)

data(geopotential)

ggplot(geopotential[date == date[1]], aes(lon, lat, z = gh)) +
    geom_contour(color = "black") +
    geom_contour(aes(x = ConvertLongitude(lon)))

map <- setDT(map_data("world"))
map[, c("lon", "group2") := ConvertLongitude(long, group, from = 180)]

ggplot(map, aes(lon, lat, group = group2)) +
    geom_path()